The present invention relates to electrode structures for use in acquiring a biosignal from a fetus. More particularly, the present invention relates to such electrodes which are introduced into body tissue by a rotary motion.
U.S. Pat. No. Re. 28,990 to Edward H. Hon and Robert W. Hon discloses an electrode system for monitoring fetal heartbeat wherein a retaining coil mounted on a holder member is rotatably introduced into a fetal epidermis by a flexible drive tube rotated by hand. The retaining coil on its holder together with the drive tube are slidably and rotatably disposed in a guide tube which is inserted through the woman's vagina and cervix.
In order to render such a device easier to use, it is desirable to eliminate the need for the drive tube to be rotated manually. In U.S. Pat. application Ser. No. 21,550 filed Mar. 20, 1979 in the name of Edward D. Hon, a plunger is mounted within the guide tube and, when moved toward the forward end of the guide tube by a force supplied thereto by the physician, causes a helical thread-type means to rotate the holder and the spiral retaining coil into a fetal epidermis. However, helical drive mechanisms are relatively complex and expensive to manufacture.